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Date: Sun, 20 Apr 2003 17:37:57 +0200
From: Andreas Pflug <Andreas.Pflug@web.de>
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To: Tom Lane <tgl@sss.pgh.pa.us>, pgsql-performance@postgresql.org
Subject: Re: [SQL] Yet Another (Simple) Case of Index not used
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Tom Lane wrote:

>It would be counting the wrong thing.  auto-vacuum needs to know how
>many dead tuples are in a table, not how many live ones.  Example:
>UPDATE doesn't change the live-tuple count (without this property,
>I don't think the sort of count maintenance Kevin is proposing could
>possibly be efficient enough to be interesting).  But it does create
>a dead tuple that vacuum wants to know about.
>
>  
>
I understand your point, but is this about VACUUM only or VACUUM ANALYZE 
too? People wouldn't bother about big databases if it's still fast 
(until the disk is full :-)

Do dead tuples affect query planning? I thought the plan only cares 
about existing rows and their data patterns.
So count(*), pg_stat_all_tables.n_tup_ins, .n_tup_upd and .n_tup_del all 
together can make a VACUUM ANALYZE necessary, right?

Regards,
Andreas